This shows the problems with the use of the JSONObject.NULL class by the Grails JSON converter

JSONObjectNullSpec.groovy

package grails.converters.tests

import grails.converters.JSON
import org.codehaus.groovy.runtime.typehandling.GroovyCastException
import spock.lang.Specification

/**
 * Created by Angel Ruiz.
 */
class JSONObjectNullSpec extends Specification {

    def "problems examples with JSONObject.NULL"() {
        given:
        def jsonPayload = JSON.parse("{'myValue': null}")

        when: "this shows that if we expect a String but for whatever reason our json payload contains null"
        String myValue = jsonPayload.myValue

        then: "myValue will be \"null\""
        myValue == "null"

        when:
        myValue = jsonPayload.myValue
        def isValueSaved = false
        if (myValue) {
            // save to DB
            isValueSaved = true
        }

        then: "the validation does not work because I have casted it to String which is what I normally expect"
        isValueSaved == true // This means the String "null" has been saved to the DB

    }

    def "other problems with JSONObject.NULL casting"() {
        // Important! This particular use case cannot be fixed with my workaround because the ideal solution would be for the JSONObject.NULL disappear an get replaced by null
        when: "this shows that if you are expecting an array list but for whatever reason our json payload is null you get an exception"
        def object = JSON.parse("{'myList':null}")
        List myList = object.myList

        then: "Fails because JSONObject.Null cannot be implicitly casted to anything but Object."
        thrown(GroovyCastException)
    }
}